Liquid crystal display devices are thin and lightweight, compared with CRTs (Cathode Ray Tube), and have an advantage that the liquid crystal display devices can operate with low operation voltage and low power consumption. For this reason, the liquid crystal display devices are employed in various electronic appliances such as a television (television receiver), a notebook-size PC (Personal Computer), a PDA (Personal Digital Assistance), and a cellular phone. These electronic appliances often carry out display of a moving image on a liquid crystal display device. For this reason, it is demanded for such a liquid crystal display device to have a high response speed in order that a moving image can be successfully displayed.
The liquid crystal display device having a high response speed that has been particularly considered noteworthy is an OCB (Optically self-Compensated Birefringence) mode liquid crystal display device. The OCB mode liquid crystal display device includes, for example: two glass substrates sandwiching liquid crystal molecules therebetween, which glass substrates have been subjected to an alignment process so that the liquid crystal molecules are aligned parallel in an identical direction; wave plates each provided on a surface of each of the glass substrate; and polarizers each further provided on the each of the substrates so as to establish crossed Nicols. The wave plates to be used may be negative wave plates whose main axis is hybrid-aligned.
FIG. 17 illustrates an operation mechanism of a conventional liquid crystal display device employing the OCB mode.
In the liquid crystal display device as illustrated in FIG. 17, alignment of liquid crystal molecules in a liquid crystal layer 13 is controlled by a voltage applied between (a) a counter substrate 12 provided on a side of an upper glass substrate 11, which side faces the liquid crystal layer 13 and (b) a pixel electrode 14 provided on a side of a bottom glass substrate 16, which side faces the liquid crystal layer 13. That is, the liquid crystal molecules constituting the liquid crystal layer 13 are maintained in splay alignment as shown in (a) of FIG. 17 while no voltage is being applied between the counter electrode 12 and the pixel electrode 14. While a voltage is being applied between the counter electrode 12 and the pixel electrode 14, the alignment of the liquid crystal molecules are changed from the splay alignment into bend alignment.
In the OCB mode, the following technique has been known as an effective technique for surely causing the liquid crystal molecules to be changed from the splay alignment into the bend alignment (hereinafter referred to as a “splay-to-bend transition”). That is, a local electric field is caused in the liquid crystal layer during the transition so as to form transition nuclei that facilitate the splay-to-bend transition. Such a technique for surely controlling the splay-to-bend transition by forming transition nuclei due to a local electric field is disclosed, for example, in Patent Citations 1 through 4.
Patent Citation 1 discloses a liquid crystal display device in which an opening is provided in a pixel electrode that is formed so as to overlap a storage capacitor electrode and transition nuclei are formed due to an electric field supplied from the opening into a liquid crystal layer. Patent Citation 2 also discloses a liquid crystal display device similar to the one disclosed in Patent Citation 1.
Patent Citation 3 discloses a technique for forming transition nuclei by a transverse electric field caused between a signal line and a pixel electrode. Further, Patent Citation 4 discloses a technique for more surely controlling the splay-to-bend transition by increasing an intensity of a transverse electric field by forming a wiring electrode between adjoining pixel electrodes.
Furthermore, Patent Citation 5 discloses another technique for surely controlling the splay-to-bend transition. That is, it is disclosed that an electrode for preventing an inverse transition is provided in an unobservable region so as to (i) prevent that molecules that are not changed from splay alignment into bend alignment remain during the splay-to-bend transition and (ii) prevent that liquid crystal molecules that have been changed into the bend alignment are inversely changed into the splay alignment.
Further, it has been known that formation of a pixel electrode on a plane base is effective for avoiding alignment failure of liquid crystal molecules. Patent Document 6 discloses a technique as follows: A pixel electrode is provided so as to overlap a respective of lines so that an aperture ratio is improved. Meanwhile, an interlayer insulating film is provided between the pixel electrode and the respective of lines so that the pixel electrode is provided on the interlayer insulating film as a base, thereby avoiding alignment failure of liquid crystal molecules.
Citation List
Patent Literature 1
Japanese Patent Application Publication, Tokukai, No. 2003-107531 A (Publication Date: Apr. 9, 2003)
Patent Literature 2
Japanese Patent Application Publication, Tokukai, No. 2005-31680 A (Publication Date: Feb. 3, 2005)
Patent Literature 3
Japanese Patent Application Publication, Tokukai, No. 2002-207206 A (Publication Date: Jul. 26, 2002)
Patent Literature 4
Japanese Patent Application Publication, Tokukai, No. 2002-350902 A (Publication Date: Dec. 4, 2002)
Patent Literature 5
Japanese Patent Application Publication, Tokukai, No. 2002-311456 A (Publication Date: Oct. 23, 2002)
Patent Literature 6
Japanese Patent Application Publication, Tokukaihei, No. 11-119261 A (Publication Date: Apr. 30, 1999)